Aims to limit the deterioration of collection objects that occurs over time, and reduces the likelihood for more invasive conservation. To limit the deterioration the team controls the environment in which the objects are displayed. There are key ‘agents’, which cause irreversible damage to the objects in our care. We deploy different techniques and materials to fight against these so called agents of deterioration.
No matter how good the standard of preventive conservation, it can only slow the rate of deterioration, it cannot stop it. This form of conservation involves sensitively working with the object to stabilise and repair deterioration. The aim and ethic is that no treatment should be undertaken which is more extensive than necessary and any intervention should aim to be reversible.
Throughout the recent national lockdown, the team has been busily preparing for our visitors’ return. Each property has its individual conservation challenges, requiring different techniques and conservation materials to minimise the effect of time. Below are some techniques we use to protect our collections against just three agents of deterioration.
The fight against pests
Wooden beams, ceilings and walls are brushed down using long-handled natural-haired brushes, gently removing built up dust without damaging the delicate plaster or paintwork. Brushing the wooden beams also disturbs any insect pests and their larvae, which may be getting ready to munch their way into the beams. Beetles, such as woodworm and deathwatch beetle, fly into buildings through open doorways and gaps in window frames. They lay their eggs on an uneven wooden surface, where they can hide them from harm. The larvae will hatch after two to three weeks and eat their way into the wood. Woodworm can live inside wood for three or more years and deathwatch beetle for up to ten years. During this time they will continue to eat the wood. When they pupate (turn into their adult form) they leave through their original entry hole and lay their own egg before flying away. Their life cycle then begins all over again. Whilst you will only see their entry holes on the outside, over time the inside of the wood resembles honeycomb and leaves the wooden object irreversibly damaged. By dusting, and therefore disturbing any eggs, we aim to prevent the initial hatching process. If we find an infestation has taken hold the Collections Care team will treat the area using a conservation grade insecticide, injecting it straight into the holes. I’m sure you can imagine how long this takes!
The furniture in our care is just as susceptible to insect pest damage as the buildings themselves. If an infestation takes hold, and the item is under a particular size, another option is open to the team. Freezing offers a safe method for eradicating insect pests in various materials; dry wood, textile, leather and paper can all be placed in freezing conditions (-20°C). When freezing wooden furniture, it is important to fully inspect and photograph the object to decide if it’s appropriate to freeze it. If it is judged to be appropriate it’s then wrapped and sealed inside plastic to protect it against the ice crystals and cross contamination in transit. Once inside the freezer treatment times can vary according to size and material type but research shows that exposure of between six to fourteen days will be sufficient. After this initial freezing process the object is removed and placed in a stable ambient environment for 24 hours to reach room temperature. The freezing process is then repeated once more before again spending time in a warm environment to thaw. The plastic is then removed and closely inspected to check for the bodies of insect pests that may have tried to escape. The whole object is then cleaned using a natural bristle brush.
Textiles are also highly susceptible to pest activity. This image shows a moth infestation within a replica pillow which was filled with feathers. To limit the likelihood of insect pest infestations the Shakespeare Birthplace Trust is in the process of limiting the use of natural fibres in its properties, along with limiting the display of collection objects incorporating textiles. All insect pests prefer animal sourced textiles, like wool, rather than plant sourced, like linen. Although as this photograph of a replica bed cover, made from synthetic material shows, they are not averse to having a little nibble! All museum insect pests prefer to be undisturbed, the team regularly inspect and move textiles, which prevents infestations from occurring.
Relative humidity and temperature
Damp conditions, such as rising damp, can cause mould on furniture and interior walls. Good ventilation and stable environments are key to ensure our houses and objects are conserved. We monitor this by reading and controlling levels of relative humidity and temperature. Relative humidity is identified as the percentage of water vapour in a space relative to the maximum amount the space is capable of holding. Air is capable of carrying higher levels of water the warmer it gets, conversely cooler air can carry less moisture. I’m sure we have all felt the effects on our hair when holidaying in warmer countries. As our hair is organic material, imagine how the same humid atmosphere affects the wooden furniture in our care.
Fluctuations in relative humidity will cause organic objects to repeatedly expand and contract, causing warping and cracking. Research shows that whilst a stable environment is best, most types of objects can withstand small changes in relative humidity. It is generally when an object is exposed to extreme changes that damage can occur.
Many individual objects are composed of a mixture of both organic and inorganic materials. An example of such an object would be a chest, made from wood, but with metal hinges and nails or screws. The ideal relative humidity for metals is low; whereas the ideal relative humidity for organic materials is higher. Therefore we have to compromise, and aim for a stable relative humidity between 40% and 65%.
The Shakespeare Birthplace Trust displays many different types of objects within its houses. Whilst some are in specialist cases, which protect against the environmental conditions, most objects are on open display. It’s important to the Shakespeare Birthplace Trust that visitors experience the houses as ‘homes’, so visitors can experience interiors as they would have been in Shakespeare’s time. Most metal objects on display are in or near fireplaces, because they were originally used for cooking. These spaces, when the properties were lived in, would have been hot and dry spaces. As fireplaces are not currently in use, they are now one of the dampest environments in which we display objects. This means our metal objects require extra protection to prevent damage. It is important to remove any dust deposits, which harbour damp and cause rust. Depending on what type of metal the object is made from, it may be appropriate to remove small areas of rust using the finest grade of steel wool. The object is then cleaned using white spirit, and a fine coat of microcrystalline wax is applied to the whole surface. This specialist wax creates a barrier between the metal and the atmosphere. When the object is put back on display it will either be placed away from the damp area or raised off the floor using a type of foam called plastazote, which does not readily absorb liquids, again this creates a barrier and provides added protection.
Whether we are fighting against dust, pests, or the effects of environmental conditions, you will often find the Collections Care team working within the Shakespeare Birthplace Trust’s properties. Whilst sometimes we need to give our full attention to our task (please don’t ask us a difficult question when we are moving a 500-year old jug) we are happy to share our knowledge in collection care. Maybe we could help you to look after your treasures?